This invention relates to an electric circuit breaker that includes electromagnetic means for opposing the magnetic contact-repulsion forces developed when a high current flows through the circuit breaker. This type of circuit breaker is referred to hereinafter as a circuit breaker with electromagnetically-assisted closing means.
A circuit breaker with electromagnetically-assisted closing means is disclosed and claimed in U.S. Pat. No. 3,663,906-Barkan et al., assigned to the assignee of the present invention, and the present application discloses and claims an improvement thereof. The circuit breaker of the Barkan et al patent comprises a first contact and a second contact movable into engagement with said first contact to close the circuit breaker and movable out of engagement with said first contact to open the circuit breaker. Electromagnetic-assist means develops a magnetic closing force on the movable contact which varies directly in accordance with the current through the contacts. This assist means of the patent comprises conductive means in series with said contacts for carrying the inter-contact current through a loop-shaped path that comprises a pair of series-connected arms between which a repulsive magnetic force is developed that urges the arms apart when current traverses said loop-shaped path. A toggle is provided for converting this repulsive force into said magnetic closing force on the movable contact. In so converting the repulsive force, the toggle also amplifies this force to provide a closing force substantially higher than the repulsive force.
The above-described arms of the loop-shaped circuit of the Barkan et al patent and the conductor section joining them are made of flexible conductive braids. A disadvantage of this construction is that in a high current application, e.g., one subject to steady state currents of 2,000 amperes or more, the volume of the braid required to carry the high current is so great as to make it very difficult to permit a reasonable size loop to be formed in the loop-shaped conductive path. Also, one of the heavy conductive arms in such a construction is required to move with the movable contact rod, and this detracts from the desired low mass of the moving contact structure.